Barack Obama has taken a big step towards preserving one of the world's natural wonders, banning uranium mining on 1m acres of land around the Grand Canyon.

The move, announced by the interior secretary, Ken Salazar, at a film screening in Washington, bans new mining claims around the canyon for the next 20 years. The area is rich in uranium deposits.

"A withdrawal is the right approach for this priceless American landscape," Salazar said in his speech. "People from all over the country and around the world come to visit the Grand Canyon. Numerous American Indian tribes regard this magnificent icon as a sacred place, and millions of people in the Colorado River Basin depend on the river."

Environmental groups said the move, which was opposed by the mining industry and some Republicans, would secure Obama's environmental legacy.

The measure does not affect some 3,200 existing mining claims around the canyon, however. The administration said there would be continued development of 11 uranium mines.

Conservation groups said Obama had shown political courage in going ahead with the ban in the face of opposition. "Despite significant pressure, the president did not settle for a halfway measure," said Jane Danowitz of the Pew Environment Group.

In the final years of the George Bush presidency, when uranium prices were rising worldwide, mining companies filed thousands of new claims in northern Arizona on lands near the Grand Canyon. They also proposed reopening old mines adjacent to the canyon.

Salazar ordered a temporary halt to new claims in 2009 after Obama came to office.

Government officials proposed the 20-year ban in October last year, after an environmental review, calling for the preservation of an "iconic landscape".

"It is appropriate to pause, identify what the predicted level of mining and its impacts on the Grand Canyon would be, and decide what level of risk is acceptable to take with this natural treasure," Bob Abbey, the director of the US bureau of land management, said at the time.

Republicans, including the former presidential candidate John McCain, condemned the move to withdraw lands from new mining claims as an emotional overreaction.

"This withdrawal is fuelled by an emotional public relations campaign designed by some of the same environmental groups whose long-time mission has been to kill mining and grazing jobs on the Arizona Strip, as well as tourism jobs at the Grand Canyon," McCain told a hearing in Congress last year.

But Gene Karpinski, president of the League of Conservation voters, argued on Monday that it made much more economic sense to protect the tourism industry that depended on the canyon.

"Extending the current moratorium on new uranium mining claims will protect tourism-related jobs, drinking water for millions downstream, and critical wildlife habitat," Karpinski said.

Conservation groups have long argued that mining laws in the west are antiquated – giving companies free access to vast swathes of public lands.

In the case of the Grand Canyon, the concerns go far beyond just conserving a spectacular view. At least one creek in the national park is known to be contaminated by uranium, and the government's environmental impact review found high levels of arsenic from old uranium operations as well as contamination of the Colorado river.